I have TB 17 and it was working fine untill yesterday and when I open it today my onion skin stopped working. Even the handles on the timeline are gone.
I’ve tried clicking on + and - (to add and reduce drawing to onion skin), restarting the program, restarting my computer, opening another project, selecting “three previous” and “three next drawings” on View>onion skin menu…nothing have worked.
Something in your user preferences may have gotten corrupted.
While the software is shut down, remove or rename the Harmony preferences folder
and when the software next launches, it will create a new default preferences folder.
C:\Users[your username]\AppData\Roaming\Toon Boom Animation\Toon Boom Harmony Premium
/Users/[your username]/Library/Preferences/Toon Boom Animation/Toon Boom Harmony Premium
setting the selection box in the Onion Skin Window from “By Drawings” to “By Frames” also worked for me.